1. Field of the Invention
The present invention relates to a light-reflecting and heating type oximeter designed to non-invasively measure oxygen saturation in the blood contained in a part of a living body by using an optical sensor.
2. Description of the Prior Art
One type of conventional non-invasive oximeter is designed to continuously and non-invasively measure oxygen saturation in the blood contained in a part of a living body by using an optical sensor. This type of optical oximeter utilizes the relative difference between the light absorption coefficient of Hb (deoxygenated hemoglobin) and that of HbO.sub.2 (oxygenated hemoglobin). More specifically, two light beams having different wavelength are directed to and transmitted through a part (finger, ear or the like) of a living body. The two different kinds of transmitted light are received by means of photosensors and the oxygen saturation in the blood contained in the part being measured is obtained on the basis of the ratio of two light absorption coefficients that represent the extent of the absorption of said two different kinds of light in the part of the living body being measured. Examples of this type of prior art include pulsation type oximeters such as those disclosed in U.S. Pat. No. 3,998,550 (Japanese Patent Publication No. 57-25217), E.P. application No. 83304939.8 (E.P. Publication No. 0102816; Japanese Patent Public Disclosure No. 59-16,445), U.S. Pat. No. 4,167,331 (Japanese Patent Public Disclosure No. 53-88778) and U.S. Pat. No. 4,407,290 (Japanese Patent Domestic Announcement No. 58-500432. According to these disclosed techniques, two light beams having different wavelength are directed to and transmitted through a part of a living body as described above. In these prior art oximeters, comparison is made between one state wherein pulsating arterial blood has flowed into blood vessel in the part of the living body being measured and consequently the amount of blood therein has increased and another state wherein the pulsating arterial blood has flowed out of the relevant part and the amount of blood has accordingly decreased, and information regarding light absorption by blood alone is obtained on the basis of the difference between the two states, that is, the pulsating component.
However, the above-described method has the disadvantage that, since measurement is effected using light which has been transmitted through a part of a living body, measurable parts are undesirably limited to parts with a relatively thin layer of tissue such as ears, fingers and the flat part of a newborn's foot. Therefore, it is impossible to measure arterial oxygen saturation in those parts of living bodies which do not allow measuring light beams to be sufficiently transmitted.
To overcome this problem, Japanese Patent Public Disclosure No. 52-51785 proposes a light-reflecting type oximeter which utilizes light reflected from a body part being measured so that all parts of living bodies can be measured. However, this light-reflecting type oximeter still suffers from the following disadvantage. Since measurement is effected on the premise that light is partially absorbed by the part of a living body being measured, the parts which are measurable are in practice limited to those in which blood vessels are distributed close to the body surface, such as fingers and ears. Therefore, it is difficult to detect pulsating components in other parts of living bodies, apart from fingers and ears, so that the oxygen saturation therein cannot be measured.